Pumping system with clutch and associated by-pass

ABSTRACT

This invention relates to a pumping system. The design of the system is such that bi-directional operation can be achieved using a significantly smaller and hence lighter unit than those currently available. It uses the direction of rotation of the drive shaft to control the opening and closure of the by-pass means for controllably returning the fluid to the first reservoir.

This invention relates to a pumping system

Conventionally, pumping systsms designed for two way operation have afluid return channel to allow fluid to flow back from one fluid store toanother. Generally, the return channel and the pump are controlledindependently. An example of a control mechanism for a return channel isa solenoid valve, the size of which can be comparable to that of themotor. The disadvantage of this arrangement is that incorporation ofsuch a return channel and associated control mechanism greatly increasesthe size and weight of the pump.

According to the present invention, a pumping system comprises a firstreservoir and a second reservoir; a motor coupled to a drive shaft; apump, driven by the drive shaft, for pumping fluid from the firstreservoir to the second reservoir; and by-pass means for controllablyreturning fluid from the second reservoir to the first reservoir;characterised by a clutch between the drive shaft and the by-pass meanswhereby rotation of the drive shaft in a first direction drives the pumpand disengages the clutch while the by-pass means is closed, androtation of the drive shaft in a second direction engages the clutch sothat the by-pass means is opened.

In the present invention, the by-pass means operates under control ofthe drive shaft, thereby removing the need for separate controlcomponents and so reducing the size and weight or the pumping system.

When rotating the drive shaft in the first direction of rotation,closing the by-pass means when driving the pump maximises the net rateof fluid transfer between the first reservoir and the second reservoirwhilst rotation in the second direction allows return of the fluid fromthe second reservoir to the first reservoir. This arrangement isparticularly convenient given that motors often exhibit greater torqueand power characteristics in one direction of rotation compared to theother.

Preferably, the by-pass means is adapted to be closed when the motor isidle.

This allows fluid in the second reservoir to be maintained at a higherpressure than fluid in first reservoir when the motor is idle.

Preferably, the by-pass means comprises a by pass valve.

Preferably, the by-pass means comprises a cam-follower and a cam;wherein the clutch is operative between the drive shaft and the cam; andwhereby opening and closure of the by-pass means is controlled byengagement of the cam-follower with the cam and rotation of the driveshaft.

Preferably, the cam comprises an end stop, whereby rotation of the driveshaft in the second direction causes the end stop to reach thecam-follower after the by-pass means is opened, thereby restraining thecam.

In a preferred embodiment, the clutch comprises a flexible resilientsleeve attached to the drive shaft and adapted to grip a shaftoperatively associated with the by-pass means when the drive shaft Isrotated in the second direction; and whereby rotation of the drive shaftin the first direction causes the sleeve to loosen from thesecond-mentioned shaft. Conveniently, the flexible resilient sleevecomprises a spring.

Alternatively, the clutch comprises two clutch plates; wherein eachclutch plate comprises bevelled teeth; wherein one clutch plate issprung loaded; whereby rotation of the drive shaft in the firstdirection allows the bevelled teeth to pass over each other; and wherebyrotation of the drive shaft in the second direction causes the bevelledteeth to mesh.

Preferably, the by-pass means is housed within the pump.

Preferably, the pump comprises a swash plate pump.

One benefit of a swash plate pump is that it uses a single way valve, sonothing leaks back to the first reservoir when the motor stops rotating.Nor is a gearbox required on the Motor, so reducing the size and noisegenerated in operation.

An example of a pumping system according to the invention will now bedescribed with references to the accompanying drawings in which:

FIG. 1 illustrates, schematically, a pumping system according to thepresent invention;

FIG. 2 illustrates the pumping system of FIG. 1 in more detail;

FIGS. 3 and 4 illustrate the motion of a piston within its respectivecylinder in the pumping system of FIG. 1;

FIG. 5 illustrates by-pass actuation in the example of FIG. 1;

FIG. 6 showes an alternative clutch arrangement.

FIG. 1 illustrates, schematically, a pumping system according to theinvention. A motor 1 is coupled to and drives a pump 2 which pumps fluidfrom a fist reservoir 3 to a second reservoir 4. A by-pass mechanism 5controls the return of fluid from the second reservoir to the firstreservoir, when motor rotation is reversed, assuming higher pressure inthe second reservoir.

FIG. 2 shows the pumping system of FIG. 1 in more detail. An outerhousing 6 of the pumping system is attached to a bulkhead 7 by athreaded mounting spigot 8 and a nut (not shown). The first reservoir 3is provided outside the housing 6 and fluid flows between the firstreservoir and the second reservoir 4 via an orifice in the threadedmounted spigot 8. The housing 6 contains the pump and the by-passmechanism. The pump comprises a swash plate 9 and two pistons 10, 11that run in two cylinders 12, 13. The swash plate engages the twopistons which move within their respective cylinders. The swash plateengages both pistons at diametrically opposed positions on the swashplate and each piston is held against the swash plate by a spring 14, 15respectively.

The motor 1 is attached to the housing 6. The motor is coupled to adrive shaft. 16 which in turn is coupled to the swash plate 9 via acoupling 17. The motor drives the swash plate which cause both pistons10, 11 to oscillate within their respective cylinders 12, 13.

FIGS. 3 and 4 show the motion of the piston 10 Within its respectivecylinder 12, FIG. 3 shows an extreme of oscillation, the engagedposition, where the piston is, as far as possible, driven in to thecylinder by the swash plate 9. FIG. 4 shows the other extreme ofoscillation, the disengaged position, where the piston is, as far aspossible, driven out of the cylinder by the spring 14 acting against thepiston.

From the disengaged position, movement of the piston 10 towards theengaged position causes the piston to compress fluid within the cylinder12, the fluid having been received from the first reservoir 3 via aninlet 18. Once the piston has moved past the inlet, the fluid within thecylinder is discharged to the second reservoir 4, via an outlet 19 and anon-return valve 20. From the engaged position, movement of the pistontowards the disengaged position, whereby the position is withdrawn pastthe inlet, allows the cylinder 12 to re-fill with fluid received fromthe first reservoir. Continuous rotation of the swash plate 9 causesrepetition of the engaged and disengaged piston cycle, thereby producingfluid flow from the first reservoir to the second reservoir.

FIG. 5 illustrates actuation of the by-pass mechanism in the pumpingsystem according to the invention. The by-pass 5 comprises a cam 21, acam shaft 22, a cam follower 23, a spring clutch 24 and a by-pass valve95. The by-pass valve is coupled to the cam-follower which engages thecam. Rotation of the cam in a first direction of rotation causes theby-pass valve to close thereby preventing transfer of fluid from thesecond reservoir 4 to the first reservoir 3. Rotation of the cam in asecond direction of rotation allows return of the fluid from the secondreservoir to the first reservoir.

The camshaft 22 is coupled to the drive shaft 16 via a spring clutch 24.Rotation of the motor 1 in the first direction causes the spring clutchto unwind, causing it to loosen its grip on the camshaft.

In FIG. 5 a, initial rotation of the motor 1 in the first direction ofrotation causes the cam 21 to rotate such that the cam follower 23 isretracted and the by-pass valve 25 is closed. Further rotation of themotor in the first direction causes the spring clutch 24 to disengagewhereby the cam and camshaft 22 are restrained by an end stop 26, andcontinued rotation of the motor is substantially unrestricted.

In FIG. 5 b, rotation of the motor 1 in the second direction of rotationcauses the spring clutch 24 to engage the camshaft 22, thereby rotatingthe cam 21. This causes the cam-follower 23 to adapt and, as aconsequence, open the by-pass valve allowing fluid to flow back from thesecond reservoir 4 to the first reservoir 3. The valve remains openuntil pump rotation is reversed.

In one example of a system according to the invention, the overalldimensions were 22 mm diameter and 62 mm length. The hydraulic fluidused was 10W40 motor oil which was pumped at up to 30 ml per minute atpressures of 48.3 Bar (4.8 MN/m² or 700 psi).

FIGS. 6 a and 6 b show an alternative clutch arrangement which may beused instead of the spring clutch 24. The alterative clutch 27 comprisestwo clutch plates 28, 29, both of which have bevelled teeth 30, 31. Theclutch plates are urged together, preferably by spring loading (notshown). FIG. 6 a shows the operation of the alternative clutch 27corresponding to rotation of the motor 1 in the first direction ofrotation. The bevelled teeth 30, 31 do not engage each other, insteadthey react against the urging force between the clutch plates 28, 27 andallow the clutch plates to run over each other.

FIG. 6 b shows the operation of the alterative clutch 27 correspondingto rotation of the motor 1 in thet second direction of rotation. Suchrotation causes the bevelled teeth 30, 31 to engage, thereby preventingrelative motion between the two clutch plates 28, 29.

1. A pumping system comprising a first reservoir and a second reservoir;a motor coupled to a drive shaft; a pump, driven by the drive shaft forpumping fluid from the first reservoir to the second reservoir; aby-pass for controllably returning fluid from the second reservoir tothe first reservoir; and a clutch between the drive shaft and theby-pass whereby rotation of the drive shaft in a first direction drivesthe pump and disengages the clutch while the by-pass is closed, androtation of the drive shaft in a second direction engages the clutch sothat the by-pass is opened.
 2. A system according to claim 1, whereinthe by-pass is adapted to be closed when the motor is idle.
 3. A systemaccording to claim 1 wherein the by-pass comprises a by-pass valve.
 4. Asystem according to claim 1, wherein the by-pass comprises acam-follower and a cam; wherein the clutch is operative between thedrive shaft and the cam; and whereby opening and closure of the by-passis controlled by engagement of the cam-follower with the cam androtation of the drive shaft.
 5. A system according to claim 4 whereinthe cam comprises an end stop, whereby rotation of the drive shaft inthe second direction causes the end stop to reach the cam-follower afterthe by-pass is opened, thereby restraining the cam.
 6. A systemaccording to claim 1, wherein the clutch comprises a flexible resilientsleeve attached to the drive shaft and adapted to grip a shaftoperatively associated with the by-pass when the drive shaft is rotatedin the second direction; and whereby rotation of the drive shaft in thefirst direction causes the sleeve to loosen from the second-mentionedshaft.
 7. A system according to claim 6, wherein the flexible resilientsleeve comprises a spring.
 8. A system according to claim 1 wherein theclutch comprises two clutch plates; wherein each clutch plate comprisesbevelled teeth; wherein at least one clutch plate is sprung loaded;whereby rotation of the drive shaft in the first direction allows thebevelled teeth of said two clutch plates to pass over each other; andwhereby rotation of the drive shaft in the second direction causes thebevelled teeth of said two clutch plates to mesh.
 9. A system accordingto claim 1 wherein the by-pass is housed within the pump.
 10. A systemas claimed in claim 1 wherein the pump comprises a swash plate pump.